Metal cleaning composition



Patented May 4, 1948 Jen: Shoemaker SenidLNo. 496,50!

team; (01. amiss):

This invention relates. to cine matter an'd to aprocessfoii fsolution'fo'r remcvallof oXid "etals' have been treated in. ai niolt 7It. Hath prising sodium" hydifoxiiiei sodi'llmf liifi'lati preferablycontaining a? small amount of. siidiiiiii; chloride; I

In my joint application; Serial" 43111168,, fi ed; Febr uary16; 1942"mewatanaon dij' the'refi'si'dis closed the use'ofa'ni o11 salt @1211 aman" alkali metal nyaroxiae all: N trate, and" preferably aismalla V akali'metal'chloride rtscieamh" "ni'et' Fsinf and particularly f rrous?iiietal crapes process comprises immersing. the. metal articleih themolterisalt bathorithe. tove rhemiqnea coin position; followed by. animmersion iii a diliite mineral acid'sucli ashsiarbcmonbior:SiHfiIILQa-Cid'. In the first step oftlie process, whichi'fiiihier'sion, in the molten salt bath orizfanic'limnni itieson themetal surface are oxidized'and} therefore lie-- moved;v and the iiiolgiilio impurities; such a graphite, carbon, and cofiinoundslcfi sulphur;silicon, phosphorus, etc. are conven d into-com pounds which'are readilyremoved: from themetah surface) in the. dilute acid treatment. Treatmentin the aqueous acidsolntion removes all the-im purities from the surfaceat the metal. and ten-- ears the metaiisurrace clean" aneitrightl Inmyappn atio serraiito, i'z313191gfiiefe Jana my 23, 1943 ev d s s e r msesem ing metal surfaces with protectiigelead alloys immersion of thearticle in a salt bath de--" scribed above, fonow'ee Ltpby trea -Itmentin: a:

dilutev mineral acid, washing or the dilutemineretacid' from the surfaceotthemetal, and finally coating the metal surfacewith aproteetizvc"1336i alloy. The salt bath and acidtreatmentstogether: convert theexposed surfaces of the metal pieces into etched matrices having minuteforamina or pockets materially depleted of oiddized and nonmetalsubstances; The etched matrices: oletained have been: found to; form an;exceeclingly strong bond with high-lead alloys when the alloy issuitably applied thereto-; H p I In my joint application Serial No;; 43-..12i-," filed: April 10, 1943- (now abandoned), isdisclosed anew typeof bearing and a process tor preparinathe new type of bearing in which;acomhinatten; 0t

molten salt and acid treatmentis used-toprepare a bearing back toreceive a bearingalloy,

In all of these processes it isnecessalfy totreat; the surface of metalwhich has-been immersed-in 1 the molten salt bathin an aqteousacidsolution. This treatment in acid solution is not entirelya ui ena themes cid? to be lietained on the a -t'e'fiifency smftioeofth I eflect" on meter coating treatmentsi It appearsitliaif' avert" a briefimmersio in di'lnte acid resultsonly iii af' remote: oi the oxide formerthemetal snrface: by the molten saltt- Hath; that some' or the-carboanegraphitemwhe eta ibntl'below the surface isex i pdserBcausinef thetobesmi-idgm siich aisurfaGe-is nnsiiitahlefof coating operations;-Fiiitthermore; iif-hasbeefi found on certain types of restatemenarticles that-even} a brief treat- 7 meat in? dimes sci-d5 resultsinstrong:

ease ior hydro en on the surface or the efiibfittlhieiit" the metalarticle; and thus for these typesof" rerroh imetar articles the proc-63S?" mamma -ale; Thehydrogen adsorption tefri'cis to wetikenthehond'between the metal and;

the? coating" alloy; Also, When} the process is used for reparinghearings; the hydrogen adsorption.

' on the bearing backresnltsiina weak band be tween the: bearing metal?alloy; and: the bearing been Inthe case'of treatment of common-meterarticles; it has, been foiirid that fairly prolonge treatmentinthedilute'aci'd'isnecessary to'remove" all of the oxide, coatin and thispickling. pro cezinrehas proved"undesirable;

It? is an object; therefore of this. invention" to pid'viideflaprocession preparing the surface of mecais foncoatin'g opeigatiorisfbyuse; of molten salts without use of acid solutions; toremoizetheonee-rayerrqrmearmuh molten Salli balth'.

Anothefobje'ctis 'tiipro'vide'a procession clean,

' ingmetfill 'rti has by" reatment'ma molten. salt,

batl ii comprisn gi sodium hydroxide.- sodium Iiitr'ate; and? plfeirblyContaining a small. alilburlfi of spaiiihi; clilori' e: wimout thesubsequent use.

I of dill itemiifiralT'abids...

Another objefit of iriveiitioriis to. pioiiideia processlffoi t costume;fiietala'rticles which the metal? oleispreparedtofiieiizethefiietalcoat; mg; 155? iii a; molten Salt. bathincluding; an; alkaliiii'etalhirdiokide and nitrate without the use ofhe: someone: twemov the oxides from. the; s'fiifac' of; th metalsv afterimmersion in m' 'm itn salt bath. l l H A ti'otlief olij eel; a newcomposition of matter suitable; when dissolved in water for removal oioxides formed on metal. articles which have been immersed in a moltensaltz bath comprising an alkali metal h droxide an alkali metal nitrate,and pre' ferably a sm-allamount of an alkali metal chloride; 7 v p rmetal? lf his'acid -lias-adeleterious Still another object of myinvention is a process for avoiding the use of acid solutions in thepreparation of bearings by a process in which the bearing base is firstimmersed in a molten salt bath, followed by immersion in a molten metalbath for providing the bearing base with a high lead tinning alloy, A

My invention has forfurther objects such adi ditional operativeadvantages and improvements as may be found hereinbelow.

dilute acid to remove the oxide layers frommetal articles immersed inmolten salt baths ifthe 12140111 1.. solution is replaced by an aqueoussolution ofa; composition comprising sodium hydroxide, sodi;

. I have found that I may avoid the use of hibited-a dull, dark finish,The metal parts were um borate, sodium cyanide, and in-somecases a smallamount of either sulfur or sodium chlolthen immersedin an aqueous bathcontaining 70 parts sodium hydroxide, 18 parts sodium cyanide, 4 partspowdered borax, 4 parts sulfur, and 4 parts-sodium chloride, made up toabout 1.5

specific gravity and heated to 250 degrees F., and

ride, or both. This composition serves the same.

purpose as the dilute acids for removing the oxides and oxidizedsubstances from the surface of the metal, but it has the advantagethatthe solution is alkaline and thereby any possibility of hydrogenadsorption or acid retention on the surfaces of metals is completelyavoided.

In general the composition may vary over fairly wide limits. The sodiumhydroxide may range from about 50 to about 90 parts, sodium borate fromabout l to about 10 parts, sodium cyanide from 5 to 46 parts, sulfurfrom .10 to about' l parts, and sodium chloride from .10 to about 4.

parts. The sodium hydroxide, sodium b orateand sodium cyanide arenecessary components of'the mixture, but the composition will operatewithout the use of sulfuror sodium chloride. However,

the'prese'nce of either of these two substances,"

and preferably both of them, appears to "have a beneficial action'on thecomposition. f a

O'ne' composition which hasbeen particularly advantageous contains 70parts sodium hydroxide, 18 parts sodium cyanide, 4 parts powdered borax,4 parts sulfur, andi parts sodium chloride. This compositionhas beenused to treat a wide variety of met rar'uues such as cast iron, springsteel, stainless "steel, and other common ferrou's'metal alloys withgoodIsucc'ess.

It has also been used with bro'nt'e, brass, and like alloyssuccessfully.

While I have particularlydescribed the'sodium compounds, it will beobvious to those skilled in the art] that any of the other alkali metalsalts, such as potassium or lithium salts; may be used in makin up thecomposition.

In practice, the composition is ter in a concentration about 8'poundspergallon of water and heated to a temperature of about 220 -250 degreesF., but of'course below the boiling point of the solution. After themetal articles have been immersed inthemolten salt bath and have beenrinsed with wash "water, they are immersed in this aqueous solution fora' period of time sufficient to removethej oxide layer formed in themolten salt bath. The period of immersion will vary over wide limits andwill depend'to a considerable extent upon the conditioner themetalsurfaces and the type, of metal beingtreat ed. In general, however,a period of minutes has been found to be satisfactoryin the usuali typeof articles. In the case ofthe treatment of bearings to prepare them toreceive a tinning alloy, a period of minutes has been foundsatisfactoryfor the average type of small bearings. It appears that thiscomposition has a dissolving action on the metal oxides and otheroxidized substances on the surface of the metals, It is alkaline and hasa reducing action to aid in dissolved in wawere maintained in this bathfor about 15 minutes.

After this treatment, the oxide layer was removed, and the articles hada metallic appearance, appearing to be ,clean' of all surfaceimpurities. 7 All oxidizable' substances, .including carbon and graphiteand compounds of sulfur,

found to be] silicon, phosphorus, etc.'were removed from the surfaces ofthe metals; These parts were then dipped in a molten lead alloycontaining about 90 percent lead, 5 per cent tin, and 5 per centantimony. The lead alloy, made: a particularly firm bond on.thesearticles, and were'satisfactory in .all respects, being'free ofpinholes, and havingauniformly coated surface. The articles showed noevidence of hydrogen embrittlement as would havebeen found if ana'cidtreatment had been used to remove the oxide layer.

In' another specific. example of my invention I'applied my process tocertaincast iron parts. These parts presented a. diflicult problem astheir surfaces held a' considerable amount of adherent or"i mbedded"si1ica".. The parts were first immersedfor-five'minutes in the moltensaltbath of the same composition as that used in the preceding example,They were then removed, rinsed, and immersed in an aqueous solution ofthe'same composition described in the preceding example, and maintainedat about 2'70 degrees.

for about 20 minutes. Finally, they were taken out, rinsed, and dried;and were found to'be particularly clean and suitable ,for'coatingoperations. After dipping, the partstin a molten lead alloy containingabout 90; per cent lead, about 5 per cent tin,: and about 5 per centantimony, they acquired a'uniform lead alloy surface free of pinholesand having no rivulets or dewetting. The bond'betweenthe Coating leadalloy and the cast iron was particularly firm.

In still another example of my invention, a cast iron bearing back wassubjected to the same treatmentnoted in the "previous example. Afterthe lead alloy surface had been put on the bearing back,- th'eEba'se wascoated witha bearing metal c'ontaining'about 1 per centtin, l per centarsenic, 15 per cent antimony, and the remainder lead, by pouringthe-molten bearing alloy on the bearing base to the desired thickness.This bearing was very satisfactory and had a-very high shear strength.-After' the bearing was poured and solidified, it was annealed accordingtothe ordinary' practice. The bearing prepared in this fashion withstoodth'e annealing opera- "tion with-out loosening of the bearing alloy fromv, 1 The use of thiscomposition in connectiQn with the" molten salt bathtreatment has several advantages. Because it is alkaline there can be nohydrogen adsorption on the surface of the metals, and thereforenohydrogen embrittlement and no deleterious action through retention ofa small amount of acid on the surface of the metal. Furthermore, thecomposition has no tendency to attack the metal itself and therefore itdoes not expose additional graphite, carbon, or other impurities whichare in the metals themselves but beneath the surface of the metal,

Its only action is a reducing action in removing the metal oxides andother oxidizable substances from the surface of the metal.

While I have described my invention hereinabove with respect toparticular applications and compositions and noting specific examples ofalloys, it will be obvious to those who are skilled in the art that theinvention is not limited to the specific examples of practice, but may:be variously practised and employed within the scope of the claimhereinafter made.

What I claim is:

A metal cleaner comprising an aqueous solu- 6 tion of an alkali metalhydroxide, an alkali metal borate, and an alkali metal cyanide, inproportions, by weight, of 50-90 parts, 4-10 parts, and 546 parts,respectively.

HUGH G. WEBSTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

